A user equipment (UE) existing in a cell of a cellular communication system connects to a base station (BS), receives control information for data communication from the BS, and transmits and receives data to and from the BS, resulting in communication between the UE and the BS. That is, since the UE transmits and receives data to/from the BS, the UE must transmit data to the BS and then the BS must transmit the received data to another UE in such a manner that data communication between one UE and another cellular UE is achieved through the BS. In this way, since one UE can transmit data to another UE through the BS, the BS schedules channels and resources for data transmission/reception and transmits channel and resource scheduling information to each UE.
Device-to-Device (D2D) communication establishes a direct link between user equipments (UEs) such that voice, data, etc. are directly communicated between UEs without passing through an evolved NodeB (eNB). D2D communication may include UE-to-UE communication, Peer-to-Peer communication, and the like. In addition, the D2D communication can be applied to Machine-to-Machine (M2M) communication, Machine Type Communication (MTC), etc.
D2D communication has recently been used as one method for solving BS loads caused by rapidly increasing data traffic. For example, differently from the legacy wireless communication system, D2D communication enables data to be communicated between two or more devices without passing through the BS, resulting in reduction of network overload.
In addition, with the introduction of D2D communication, the number of BS procedures is reduced, power consumption of devices that participate in D2D is reduced, the data transfer rate is increased, the network accommodation capability is increased, and load dissipation and cell coverage extension are expected.